The present invention relates in general to telecommunication equipment and in particular to a new and useful system for conducting a videoconference between a plurality of participants who are physically present at different locations.
A comprehensive review of the prior art in this field is given in the German publication Kommunikations-Endgerate Grundlagen, Verfahren, Bausteine, Gerate, Systeme (Communication Terminals-Fundamentals, Methods, Building Blocks, Systems) by Friedrich Ohmann, Springer publishing house, Berlin, Heidelberg, New York, Tokyo 1983, chapter 7.5 "Bildkonferenz" (Videoconference) pages 414-423. According to that source, what is required of such conferences is that all subscribers (interlocutors/participants) see and hear each other during the whole time-simultaneously, and in the correct direction, and be able to show one another written documents and objects. Besides the minimum technical equipment necessary at every location for carrying out the conference, the costs of terminals and their interconnections increase in an unjustifiable proportion with the number of interconnected locations, if no particular measures are taken, yet all of such measures have their advantages and disadvantages.
To reduce these costs, particularly such as relate to the taking, transmitting, and reproducing of pictures, measures such as parallel processing and switching, and mixed forms developed therefrom, may be provided. With the first mentioned measure, the number of needed terminals and channels can be reduced, but always several conference participants are required to be present together at the location. With the other means, a single picture must always be transmitted to all of the interlocutors, and while no full interconnection is required, nevertheless a continual voice-controlled or manual switching is necessary, preferably by one of the participants.
A solution, considered trivial, and requiring everyone of the participants to be equipped with complete terminals, such that picture and sound from one participant is transmitted individually to all other locations of the conference and there reproduced with an individual loudspeaker and screen, must certainly be rejected as unjustifiably expensive. That is why prior art videoconferencing systems have been limited to arrangements where the interlocutors are concentrated at two locations between which a point-to-point communication for picture and sound in the two directions is established (studio conference, committee room conference). Even in systems designated "working place conference", the main communication, for example through a public network, is established between two localities, with the individual working places being in the same buildng or at the same location, each equipped with a minimum of terminals and being connected together within each of the localities through concentrators.
Prior art videoconferencing therefore has remained restricted to conferences between two regional groups of participants.